The present invention relates to pumps in general and, more particularly, to valve arrangements for controlling the operation of air-operated diaphragm pumps.
There are already known various constructions of pumps, among them such which are particularly suited for pumping liquids with high viscosity, such as paint or the like. Some of the known pumps are constructed as diaphragm pumps in which compressed air or similar gaseous medium is being used for achieving the pumping action. In pumps of this type, a movable wall including a flexible diaphragm extends across the internal space of the pump casing to sealingly subdivide such interior into a pumping chamber for the liquid to be pumped and an actuating chamber into which the pressurized gaseous medium is admitted to exert its pressure on the movable wall and from which it is discharged, thus to achieve the pumping action. Such diaphragm pumps are often used in tandem, that is, two of such pumps are being used at the same time, these pumps having their movable walls connected for movement in unison so that, while one of the diaphragm pumps has the pressurized gaseous fluid admitted into its actuating chamber and thus pumps the liquid, the contents of the actuating chamber of the other pump is discharged as the movable wall moves in unison with the first-mentioned pump movable wall and, hence, additional liquid is being drawn into the pumping chamber of the latter pump.
It will be appreciated that, to achieve the above-described pumping action in the pump arrangement including the two tandem pumps, it is necessary to provide for control of the admission and discharge of the gaseous fluid or medium to and from the actuating chambers of the two pumps in an organized and precisely timed manner. To this end, there have already been developed various constructions of control and/or distributing valve assemblies. However, experience with the control assemblies or arrangements of this type which have become known so far has shown that they suffer from many drawbacks. One of the disadvantages of the control or distributing arrangements of conventional constructions is that, more often than not, they need to be lubricated, which is frequently done by entraining droplets of oil in the pressurized gaseous medium. It will be appreciated that, if the pressurized gaseous medium contains any contaminants, such as particles of dust or the like, such contaminants will be captured by the lubricant and thus perform an abrading function in the valve arrangement, which will result in excessive wear of the various components of the latter.
In a copending commonly owned patent application Ser. No. 564,947 filed concurrently herewith, there is disclosed a control arrangement including two switching valve assemblies which control the admission of pressurized fluid, especially compressed air, to respective end surfaces of a distributing spool valve. As advantageous as these switching valve assemblies are in many respects, the fact remains that they are rather complicated and hence expensive.